Wireless communication method and apparatus

ABSTRACT

A method for establishing communications between a master unit and a plurality of node units. Of the plurality of node units, K node units are assumed to have established communications with a master unit. A first (K+1) node unit of the plurality of node units, desires to establish communications with the master unit. The method includes transmitting from the master unit, a base-station spread spectrum signal having a common signalling chip code, transmitting from the first node unit a second spread spectrum signal with a first identification code using the common-signalling chip code, transmitting from the master unit a third spread spectrum signal with a master unit identification code, using the common-signalling chip code. The method further includes generating at the first node unit using the master unit identification signal, a master unit chip code for transmitting spread spectrum signals to the master unit. Additionally, the method includes generating, at the master unit using the first identification code, a first node unit chip code for transmitting spread spectrum signals to the first node unit.

BACKGROUND OF THE INVENTION

1. This invention relates to spread spectrum communications, and moreparticularly to a method for establishing spread spectrum communicationsbetween a base station and a handset.

DESCRIPTION OF THE PRIOR ART

2. A spread spectrum system is one in which the signal energy isdistributed over a frequency spectrum that is much wider than themaximum bandwidth required to transmit the information being sent.Techniques for direct sequence spread spectrum modulation have beendeveloped for several years to ensure, among other benefits, securecommunications. Modulation is achieved by mixing the information to besent with a periodic pseudo-noise (PN) code. The spectral densityfunction for the resulting signal has a sin(X)/X shape with a very widebandwidth, as compared to the information, and a lower spectral densityfunction amplitude as compared to the information. This modification ofthe original spectral density function reduces the signal's sensitivityto in-band interference and jamming, as well as reducing interference toother equipment that is sensitive to radio frequencies. Among the otheradvantages inherent to a spread spectrum system are selective addressingcapabilities, code division multiplexing for multiple access, and highlyaccurate ranging capabilities.

3. Due to the encoded nature of the signal, demodulation is a moreinvolved process compared with demodulation schemes associated withtraditional communications systems. In this case, demodulation involvesa receiver reference code, identical to that transmitted, thatsynchronizes the receiver with the transmitter. The difficulty with thisprocess is that there is no indication of the degree ofnon-synchronization between received and reference codes until a veryhigh degree of synchronization is achieved. Additionally, mismatchesbetween transmit and receive oscillators used to generate PN codes tendto cause drift in the synchronization between transmitter and receiver.

4. A prior art communications system using spread spectrum for awireless private branch exchange (PBX) is described in U.S. Pat. No.4,672,658 to Kavehrad et al., issued Jun. 9, 1987, which is incorporatedherein by reference. Kavehrad et al. relate to a wireless PBX networkwherein direct sequence spread spectrum multiple access is used forvoice and data communications to support a plurality of local-local andlocal-external communications. The PBX network includes a plurality oflocal user transceivers using a first unique chip sequence pattern forinformation communication and a second common chip sequence pattern forcall set up, and a central PBX having a plurality of PBX transceiversusing corresponding chip sequence patterns.

5. The prior art does not teach a method for establishing spreadspectrum communications using a spread spectrum signal which allows theuse of one or more common signalling spectrum spreading codes to managehandshaking from a master unit to a plurality of node units, without theuse of a separate frequency channel for common signalling, and withoutrequiring a separate time channel for common signalling.

OBJECTS OF THE INVENTION

6. An object of the invention is to provide a method for establishingcommunications using spread spectrum signals to communicate between amaster unit and a plurality of remote units.

7. Another object of the invention is to provide for a method for usingspread spectrum signals to communicate between a master unit and aplurality of remote units requiring a minimum amount of digital signalprocessing.

8. A further object of the invention is to allow use of the samefrequency for both common signalling as well as communications.

9. An additional object of the invention is to allow use of the samefrequency and same time slot for both common signalling andcommunications.

10. Another object of the invention is to allow access and handshakingof a plurality of node units to a single master unit when no node unithas a-priori knowledge of spectrum spreading or identification codes,time slots, synchronization parameters, or frequencies utilized at themaster unit to be accessed.

11. A still further object of the invention is to allow use of acollision avoidance protocol.

12. Another object of the invention is to allow the management ofsimultaneous users on a single master unit on a common signalling andcommunication time slot and frequency basis.

13. Another object of the invention is to allow the node units to have aminimal need for intelligence, processing power, or local synchronizedclock sources.

14. Another object of the invention is to allow the option for usingspectrum spreading codes as address codes.

15. Another object of the invention is to allow node response to a validsignal within a time slot through CDMA, eliminating the need for ahighly accurate clock and a level of node complexity and intelligence.

16. A still further object of the invention is to allow for M-ary datatransmission to simplify transceiver complexity in remote mode units.

17. An additional object of the invention is to allow for a network ofmaster units, each communicating with a multiplicity of node units, in agrid which requires only three frequencies in a frequency divisionmultiplex operation.

18. Another object of the invention is to allow half-duplexcommunication between master unit and node unit in the same TDMA timeslot.

SUMMARY OF THE INVENTION

19. According to the present invention as embodied and broadly describedherein, a method and apparatus for establishing and maintaininghandshaking and communications between a master unit and a plurality ofN node units, with multiple configurations, is provided. Of theplurality of N node units, K node units, where K<N, are assumed to haveestablished 2K communications links with a master unit, using up to 2Kdifferent spectrum spreading codes to generate up to K different spreadspectrum signals to transmit from the master unit to K node units, and Kdifferent spread spectrum signals to transmit from K node units to themaster unit. A time slot for each of the K linked node units is providedfor transmitting and receiving in each of the first K time slots. Atotal of N time slots, constituting a time frame, are assumed availablefor communicating and/or initializing communications with the masterunit by using time division multiple access. While system capacityallows N node units to establish and maintain simultaneouscommunications, with a single master unit, the number of node units, X,which may access the master unit is not limited to N, but may be muchgreater.

20. In this invention, transmitting and/or receiving in a time slot mayinclude transmitting and/or receiving in a plurality of time slots in aslot position within a frame and/or from frame to frame. Transmittingand/or receiving in a particular time slot also does not limit a timeslot to a particular slot position within a frame.

21. A first node unit, i.e. the (K+1)th node unit, of the plurality ofthe N node units, of the plurality of X node units able to access themaster unit, is assumed to desire to establish communications with, oraccess, the master unit. The method constitutes handshaking between the(K+1)th node unit and the master unit in an access time slot.

22. A first embodiment of the present invention implements the (K+1)thtime slot as the access slot and (K+1)th communication slot. The (K+1)thtime slot may occupy, or float to, any open time slot within the timeframe of the N-K open slots, and may change time slots as the number, K,of node units which have established communications links with themaster unit, changes. This embodiment comprises several steps, the firstof which is transmitting in a (K+1)th time slot from the master unit amaster-initialization spread spectrum signal, CSn1, common to theplurality of X node units.

23. In response to receiving the master-initialization spread spectrumsignal, CSn1, in the (K+1)th time slot, the (K+1)th node unit transmitsin the (K+1)th time slot a first node-initialization spread spectrumsignal, CSm1, which may be the same as, and thus a node retransmissionof, the master-initialization spread spectrum signal, CSn1, or which maybe a spread spectrum signal having a chip code distinct from themaster-initialization spread spectrum signal, CSn1, and common to allmaster units that the (K+1)th node unit may access. The firstnode-initialization spread spectrum signal, CSm1, may contain the(K+1)th node unit's identification code as data information modulatingthe chip sequence for the (K+1)th node-initialization spread spectrumsignal.

24. The master unit receives the first node-initialization spreadspectrum signal, CSm1, from the (K+1)th node unit in the (K+1)th timeslot, and, in reply, transmits in the (K+1)th time slot amaster-identification spread spectrum signal, CSn2, which may bedistinct from spread spectrum signal CSn1 but common to all X nodeunits. The master-identification spread spectrum signal contains themaster unit's (K+1)th slot identification code as data informationmodulating the chip sequence for the master-identification spreadspectrum signal.

25. In response to receiving the master-identification spread spectrumsignal, CSn2, the (K+1)th node unit may transmit in the (K+1)th timeslot a second node-initialization spread spectrum signal, CSm2. Thesecond node-initialization spread spectrum signal, CSm2, may contain(K+1)th node-identification code as data information modulating the chipsequence from the node-initialization spread spectrum signal. Thenode-identification spread spectrum signal may have a high degree ofuniqueness to the plurality of the N−1 other node units.

26. The master unit receives the (K+1)th node unit's identificationcode, and transmits in the (K+1)th time slot a master unit (K+1)th slotcommunication spread spectrum signal, CMNk+1, generated from a spectrumspreading code derived from the (K+1)th node unit's identification code.

27. In response to receiving the (K+1)th master identification code inthe (K+1)th time slot from the master unit the (K+1)th node unittransmits in the (K+1)th time slot a (K+1)th node unit communicationspread spectrum signal, CNMk+1, generated from a spectrum spreading codederived from the (K+1)th master-identification code.

28. If all node units utilize the same receive spread spectrum code(CMNk+1), the master unit does not necessarily have to derive a spectrumspreading code from the (K+1)th node unit's identification code, but mayrather, upon determination by the master unit that the (K+1)th nodeunit's identification code is valid, transmit a spread spectrumcommunication signal common to all node units able to access the masterunit and rely on address bits within the time slot to maintainsynchronization of the node units with the master unit.

29. In a second embodiment of the present invention, a fixed, or Fth,time slot, such as the 1st or Nth slots of the plurality of N time slotsin a time frame, serves as the access slot. The second embodimentcomprises of the steps of transmitting in the Fth time slot from themaster unit a master-initialization spread spectrum signal, CSn1, commonto all node units. The Fth time slot may occupy a fixed time slot withinthe time frame of the N-K unused time slots, and does not change slotsas the number, K, of node units which have established communicationslinks with the master unit, changes.

30. In response to receiving the master-initialization spread spectrumsignal, CSn1, in the Fth time slot, the (K+1)th node unit transmits inthe Fth time slot a first and second node-initialization spread spectrumsignal, chiasm, CSm2, having the characteristics and propertiespreviously discussed.

31. The master unit receives the node-initialization spread spectrumsignal, CSm, in the Fth time slot from the (K+1)th node unit, andtransmits in the Fth time slot a master-identification spread spectrumsignal, CSn2, which may be distinct from the master-initializationspread spectrum signal, CSn1, but common to all X node units, andcontaining the master unit's (K+1)th slot identification code. Themaster-identification spread spectrum signal, CSn2, may includeinformation directing the (K+1)th node unit as to which time slot andspectrum spreading code to use for communication from the (K+1)th nodeunit to the master unit.

32. In response to receiving the master-identification spread spectrumsignal, CSn2, the (K+1)th node unit transmits in the Fth time slot thesecond node-initialization spread spectrum signal, CSm2. The secondnode-initialization spread spectrum signal, CSm2, is common to allmaster units that (K+1)th node unit may access, and may contain its(K+1)th node-unit-identification code. The second node-initializationspread spectrum signal, CSm2, may have a high degree of uniqueness tothe plurality of the N−1 other node units.

33. The master unit receives the (K+1)th node unit's identification codefrom the (K+1)th node unit in the Fth time slot, and transmits in the(K+1)th time slot a master unit (K+1)th slot communication spreadspectrum signal, CMNk+1, generated from a spectrum spreading codederived from the (K+1)th node unit's identification code.

34. In response to receiving the (K+1)th master unit identification codefrom the master unit in the Fth time slot via the CSn2 spread spectrumsignal, the (K+1)th node unit transmits in the (K+1)th time slot a(K+1)th node unit communication spread spectrum signal, CNMk+1,generated from a spectrum spreading code derived from the (K+1)th masterunit identification code.

35. If all node units utilize the same receive spread spectrum code(CMNk+1), the master unit does not necessarily have to derive a spectrumspreading code from the (K+1)th node unit's identification code, but mayrather, upon determination by the master unit that the (K+1)th nodeunit's identification code is valid, transmit a spread spectrumcommunication signal common to all node units able to access the masterunit and rely on address bits within the time slot to maintainsynchronization of the node units with the master unit.

36. As an alternative architecture in this configuration, the (K+1)thnode unit may transmit the (K+1)th node unit communication spreadspectrum signal in the (K+1)th time slot in response to receiving themaster unit (K+1)th slot communication signal in the (K+1)th time slot.In this case, the master unit (K+1)th slot identification signaltransmitted in the Fth time slot would not necessarily containinformation detailing which time slot of the N-K time slots to use forcommunication transmissions.

37. In a third embodiment of the invention, the master unit may functionwith the initialization, identification, and communication protocolsdetailed in first and second embodiments, but may be configured totransmit the master-initialization spread spectrum signal, CSn1, in aplurality of vacant (N-K) time slots. If the master unit does transmitin a plurality of vacant (N-K) time slots, then node units (K+1), (K+2),(K+3), . . . , (K+(N-K)) (or N) may access the master unit in the(K+1)th, (K+2)th, (K+3)th, . . . , (K+(N-K))th (or Nth) time slots,respectively or randomly. Therefore, the (K+1)th node unit trying toaccess the master unit would access the first time slot immediatelyavailable after its initiation of the access attempt, instead of waitingfor the (K+1)th or Fth time slot to occur in the next frame.

38. Thus, if K users are present, the master unit transmits in the 1stthrough Kth time slots the master unit communication spread spectrumsignals, CMN1 through CMNk, pertaining to the 1st through Kth nodeunits, and in the (K+1)th through Nth time slots a master-initializationspread spectrum signal, CSn1, which is common to the plurality, X, ofnode units that may access the master unit. The master-initializationspread spectrum signal may be distinct from all master or node unitcommunication and identification spread spectrum signals.

39. In all three embodiments, if a plurality of up to N-K node unitstries to access the master unit sequentially in time, with the periodbetween access attempts being greater than or equal to the slot period,upon reception of the master-initialization spread spectrum signal,CSn1, each node unit will access the open time slot availableimmediately following its initiation of the access attempt. When thefirst (K+1)th node unit has accessed the master unit (master unit slotand (K+1)th node unit identification signals are being transmitted inthe (K+1)th time slot), the master unit may wait to transmit the (K+2)ththrough Nth master-identification signals until the (K+1)th slot isoccupied with master unit-to-(K+1)th node unit and/or (K+1)th nodeunit-to-master unit communication signals.

40. If a plurality of up to N-K node units tries to access the masterunit instantaneously (the time period between node unit access attemptsbeing less than the slot period), upon reception of themaster-initialization spread spectrum signal, CSn1, each node unit ofthis plurality of node units will transmit a node-initialization spreadspectrum signal, CSm, within the same time slot, thus jamming at leastone of the node-initialization spread spectrum signals, CSm, at themaster unit. If the master unit does not receive a validnode-initialization spread spectrum signal, CSm, or identification codefrom a node unit during the time slot, it may cease to transmit anysignal in that time slot for a predetermined period of time, or it maytransmit a “jammed signal alarm” code through the master unit slotidentification signal, CSn2. When a lack of response or a jammed signalalarm code from the master unit is encountered, the node units whichtried to access the master unit instantaneously, of the plurality, N-K,of node units, may initiate a node unit internal “wait” state, whoseperiod may be derived from each node unit's identification code. Afterthe wait state period, the plurality of node units which failed toaccess the master unit may attempt to access it again. Since wait statesmay be highly unique to each node unit, it is unlikely that the sameplurality of node units will jam each other again.

41. If all N time slots are being used for communication orinitialization functions by N node units, then the master-initializationspread spectrum signal, CSn1, is not transmitted by the master unit, andno new node units of the plurality of X-N node units may access themaster unit. The master unit may operate such that the Nth time slot maytransmit a “busy” alarm to the plurality of N-K node units having notestablished communications with the master unit such that it informsthem that no further access is available at that master unit, therebyallowing only N−1 node units to access the master unit.

42. Additional objects of the inventions and advantages of the inventionwill be set forth in part in the description which follows, and in partwill be obvious from the description or may be learned by practice ofthe invention. The objects and advantages of the invention also may berealized and attained by means of the instrumentalities and combinationsparticularly pointed out in the appended claims.

BRIEF DESCRIPTION OF THE DRAWINGS

43. The accompanying drawings, which are incorporated in and constitutea part of the specification, illustrate preferred embodiments of theinvention, and together with the description serve to explain theprinciples of the invention.

44.FIG. 1 illustrates a master unit with a plurality of remote units;

45.FIGS. 2A and 2B illustrate the protocol of the method of the presentinvention;

46.FIG. 3 illustrates time slots;

47.FIG. 4 illustrates the multiple access system timing diagram of apreferred embodiment using binary signalling techniques;

48.FIG. 5 illustrates the multiple access system timing diagram of asecond preferred embodiment using M-ary signalling techniques; and

49.FIG. 6 illustrates an FDMA three frequency master unit network.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

50. Reference will now be made to the present preferred embodiments ofthe invention, examples of which are illustrated in the accompanyingdrawings.

51. The invention disclosed in this patent is related to the inventionsdisclosed in U.S. Patent Application entitled “Spread SpectrumCorrelator,” by Robert C. Dixon and Jeffrey S. Vanderpool and havingSer. No. 07/390,315 and Filing Date of Aug. 7, 1989; and in U.S. PatentApplication entitled “Asymmetric Spread Spectrum Correlator,” by RobertC. Dixon and Jeffrey S. Vanderpool and having Ser. No. 07/389,914 andFiling Date of Aug. 7, 1989, which are expressly incorporated herein byreference.

52. In the exemplary arrangement shown in FIG. 1, the present inventionincludes a method and apparatus for establishing communications betweena master unit 50 and N node units. The master unit 50 may be a basestation, PBX, file server or other central controlling device serving asthe center of a star network, and the node units may be any type ofcomputer, communications, telephone, video or other data device servingas a node point in the star network. While the system capacity allows Nnode units to establish simultaneous communications with a single masterunit, the number, X, of node units that may access the master unit isnot limited to N node units, but may be much larger than N.

53. As illustratively shown in FIG. 1, a master unit 50 is shown with aplurality of N node units 51, 52, 53, 54, 55, where N=5, and a pluralityof X node units 56, of which the plurality of N node units is a subset.Of the plurality of N node units 51, 52, 53, 54, 55, three node units(K=3), are assumed to already have established communications channelswith the master unit 50 using up to six different spectrum spreadingchip codes to generate up to six different spread spectrum signals.

54. A particular node unit and master unit use two of up to six spectrumspreading chip codes during communications. A first of the two spectrumspreading chip codes is used while communicating from the master unit tothe particular node unit. A second of the two spectrum spreading chipcodes is used while communicating from the particular node unit to themaster unit. The spectrum spreading chip codes may be embodied as apseudo-random sequence, and the spectrum spreading chip codes typicallymodulate information data which may be embodied as a data bit sequence,as is well known in the art.

55. A total of five time slots (N=5), which constitute a time frame, areassumed available for communicating with the master unit by use of timedivision multiple access. Each of the three node units 51, 52, 53,communicates with the master unit 50 in a time slot, which may be thefirst three of five time slots. Alternatively, each of the three nodeunits may communicate with the master unit 50 in three time slots whichhave any predetermined order. Additionally, a (K+1)th time slot, whichby way of example is the fourth time slot (K+1=4), may occupy, or“float” to, any open time slot within the time frame of the two unusedtime slots, and may change time slots as the number, K, of node unitswhich have established communications links with the master unit,changes. A node unit, which of the five node units is the fourth nodeunit, desires to establish communications with, or access the masterunit 50.

56. In the present invention, transmitting and/or receiving in a timeslot may include transmitting and/or receiving in a plurality of timeslots in a slot position within a frame and/or from frame to frame.Transmitting and/or receiving in a particular time slot also does notlimit a time slot to a particular slot position within a frame.

57. In a first embodiment of the invention, the apparatus and methodcomprises the steps of transmitting in a (K+1)th time slot from themaster unit 50, a master-initialization spread spectrum signal, CSn1.The master-initialization spread spectrum signal uses amaster-common-signalling chip code which is known and stored in all thenode units able to access the master unit. All of the node units havemeans responsive to the master-initialization spread spectrum signal,for correlating with the master-common-signalling chip code of themaster unit 50. The correlating means may be embodied as a surfaceacoustic wave device (SAW), digital device, or any other device whichcan perform the required function. The master-common-signalling chipcode may, but is not required to, modulate information data embodied asa data bit sequence or data symbol sequence. The information data mayinclude indexing, addressing, or other data pertinent to the (K+1)thtime slot. The entire chip sequence of the master-common-signalling chipcode may be transmitted per data bit or data symbol during the (K+1)thtime slot from the master unit.

58. In response to receiving the master-initialization spread spectrumsignal, CSn1, at the (K+1)th node unit, the method and apparatus includetransmitting from the (K+1)th node unit in the (K+1)th time slot a firstnode-initialization spread spectrum signal, CSm1. The firstnode-initialization spread spectrum signal may, but is not required to,retransmit the master-common-signalling chip code which was transmittedfrom the master unit during the (K+1)th time slot. Alternatively, thefirst node-initialization spread spectrum signal, CSm1, may use anode-common-signalling chip code which can be received by all masterunits that the (K+1)th node unit may access. The firstnode-initialization spread spectrum, CSm1, signal additionally may bemodulated by information data, such as the (K+1)th node unit'sidentification code, or an acknowledgment (“ack”) to signal the masterunit a node unit desires to establish communications with the masterunit, allowing the master to proceed with the exchange of identificationand communication information between the master unit an the (K+1)thnode unit. The entire chip sequence of the master-common-signalling chipcode or node-common-signalling chip code may modulate each bit, orsymbol, of the information data, i.e., the node unit's identificationcode, using spread spectrum modulation.

59. The master unit 50 receives the first node-initialization spreadspectrum signal, CSm1, from the (K+1)th node unit in the (K+1)th timeslot, and transmits in the (K+1)th time slot a master-identificationspread spectrum signal, CSn2. The master-identification spread spectrumsignal uses a master-identification code which is common to all X nodeunits. The master-identification code is modulated by themaster-common-signalling chip code or node common-signalling chip codeto produce the master-identification spread spectrum signal.

60. The master-identification code may be unique to the (K+1)th masterunit slot, and may be unique to a minimum of N master-identificationcodes available at the master unit 50. The master-identification code,which may be distinct from all other master-identification codes andnode-identification codes, is used by the node unit for generating amaster unit chip code for a spread spectrum signal used to communicatewith the master unit 50. The master-unit chip code is generated from analgorithm processing the master-identification code, which may include,for example, a one-to-one relationship for setting taps on a set ofshift registers.

61. In response to receiving the master-identification spread spectrumsignal, CSn2, from the master unit 50 in the (K+1)th time slot, the(K+1)th node unit transmits in the (K+1)th time slot a (K+1)node-identification code to the master unit using a secondnode-initialization spread spectrum signal, CSm2. As describedpreviously for the first node-initialization spread spectrum signal, thesecond node-initialization spread spectrum signal, CSm2, uses amaster-common-signalling chip code, or a node-common-signalling chipcode which is common to all master units to which the (K+1) node unitmay access for modulating the node-identification code. The (K+1)node-identification code may have a high degree of uniqueness comparedwith node unit identification codes by which the plurality of other nodeunits may access the master unit.

62. The master unit 50 receives the (K+1)th node-identification code,and establishes the master-unit-to-(K+1)th-node-unit communicationchannel by transmitting in the (K+1)th time slot amaster-unit-(K+1)th-slot communication spread spectrum signal, CMNK+1. A(K+1)-node-unit chip code for the master unit-(K+1)th slot communicationspread spectrum signal may be generated from the (K+1)th node unitidentification code.

63. In response to receiving the (K+1)th master-identification code, the(K+1)th node unit establishes the (K+1)th node-unit-to-master unitcommunication channel by transmitting in the (K+1)th time slot a (K+1)thnode-unit-communication spread spectrum signal, CNMK+1. A master-unitchip code for the (K+1)th node unit communication spread spectrum signalis generated from the (K+1)th master-identification code.

64. In the explanatory embodiment discussed herein, the master unit mayoperate such that it does not transmit in a time slot except to send aplurality of K master unit slot communication spread spectrum signals,CMN1 to CMNK, in K time slots, to K node units which have establishedcommunications links with the master unit, plus a master-initializationspread spectrum signal, CSn1, in the case of a search for a new nodeunit trying to access the master unit, or a master unit slotidentification signal, CSn2, in the case of a node unit being in theprocess of accessing a master unit, leaving N-K-1 time slots unused. Ifthe master unit is transmitting a master-identification spread spectrumsignal, CSn2, in the (K+1)th time slot (the (K+1)th node unit is in theprocess of accessing the master unit), it then may transmit amaster-initialization spread spectrum signal, CSn1, in the (K+2)th timeslot, in order to allow the (K+2)th node unit to access the master unitthrough the same method.

65. If all node units utilize the same receive spread spectrum code(CMNk+1), the master unit does not necessarily have to derive a spectrumspreading code from the (K+1)th node unit's identification code, but mayrather, upon determination by the master unit the (K+1)th node unit'sidentification code is valid, transmit a spread spectrum communicationsignal common to all node units able to access the master unit and relyon address bits within the time slot to maintain-synchronization of thenode units with the master unit.

66. If a plurality of up to N-K node units tries to access the masterunit sequentially in time, with the period between access attempts beinggreater than or equal to the time frame period, upon reception of themaster-initialization spread spectrum signal, CSn1, each node unit ofthe plurality of N-K node units will access the time slot immediatelyavailable following its initiation of the access attempt. When the first(K+1)th node unit has accessed the master unit (master unit (K+1)th slotand (K+1)th node unit identification signals are being transmitted inthe (K+1)th time slot), the master unit may wait to transmit the (K+2)thmaster unit slot identification signal until the (K+1)th slot isoccupied with master unit-to-(K+1)th node unit and/or (K+1)th nodeunit-to-master unit communication signals.

67. If a plurality of up to N-K node units tries to access the masterunit instantaneously (the time period between node unit access attemptsbeing less than the frame period), upon reception of themaster-initialization spread spectrum signal, CSn1, each node unit ofthis plurality of node units will transmit a first node initializationspread spectrum signal, CSm1, within the same time slot, thus jamming atleast one of the node unit initialization signals, CSm, at the masterunit. If the master unit does not receive a valid node-initializationspread spectrum signal, CSm, or identification code from a node unitduring the time slot, it may cease to transmit any signal in that timeslot for a predetermined period of time, or it may transmit a “jammedsignal alarm” code through the master-identification spread spectrumsignal, CSn2. When a lack of response or a jammed signal alarm code fromthe master unit is encountered, the node units which tried to access themaster unit instantaneously, of the plurality, N-K, of node units, maythen initiate a node unit internal “wait” state, whose period may bederived from each node unit's identification code. After the wait stateperiod, the plurality of node units which failed to access the masterunit may attempt to access it again. Since wait states may be highlyunique to each node unit, it is unlikely that the same plurality of nodeunits will jam each other again.

68. If all N time slots are being used for communication orinitialization functions by N node units, then the master-initializationspread spectrum signal, CSn1, is not transmitted by the master unit, andno new node units of the plurality of X - N node units may access themaster unit until a time slot opens up through one or more of the N nodeunits abandoning communications with the master unit.

69. As an alternative architecture to the present embodiment, the masterunit may operate such that the Nth time slot may be held in reserve totransmit a “busy” alarm to the plurality of N-K node units having notestablished communications with the master unit such that it informsthem that no further access is available at that master unit, therebyallowing only N−1 node units to access the master unit.

70.FIGS. 2A and 2B illustrate the foregoing protocol of the presentinvention.

71.FIG. 2A illustrates the case where the node unit responds to themaster-initialization signal with the node-initialization signal, whichmay be a simple acknowledgment (“ack”), to advise the master unit of the(K+1)th node unit's presence and desire to establish communications. Themaster and node units then proceed to exchange identification andcommunication signals as detailed above.

72.FIG. 2B illustrates the case where the node unit responds to themaster-initialization signal with the node-identification signal,decreasing the time and steps necessary to establish communicationsbetween the master unit and the (K+1)th node unit. The master and nodeunits then proceed to exchange identification and communication signalsas detailed above.

73. The time division multiple access frame and time slots of thepresent invention are illustratively shown in FIG. 3. There are N timeslots, with N=5, available for N node units to communicate with themaster unit, with K=3 time slots already being used by the first K nodeunits which are communicating with the master unit. During any one orall of the available N-K=4 time slots, the master unit transmits amaster-initialization spread spectrum signal, CSn1, common to the set ofX node units that may access the master unit, of which the N=5 nodeunits is a subset. Since all node units which may access the master unitrecognize the first master-initialization spread spectrum signal, CSn1,the 4th node unit trying to access the master unit will know that thistime slot is available for communicating. In response to receiving themaster-initialization spread spectrum signal, CSn1, in the 4th timeslot, the 4th node unit may transmit in the 4th time slot to the masterunit its identification code or a simple acknowledgment (“ACK”) througha first node-initialization spread spectrum signal, CSm1, common to allmaster units it may access, but distinct from the master-initializationspread spectrum signal, CSn1.

74. In response to receiving the first node-initialization spreadspectrum signal, CSm1, in the 4th time slot from the 4th node unit, themaster unit transmits its 4th master-identification code, which may bedistinct from all other master and node unit identification codes, witha master-identification spread spectrum signal, CSn2, common to theplurality of node units that may access the master unit and distinctfrom the master-initialization spread spectrum signal, CSn1, and thefirst node-initialization spread spectrum signal, CSm1. In response toreceiving the 4th master-identification spread spectrum signal, CSn2,the 4th node unit may transmit in the 4th time slot its identificationcode through the second node-initialization spread spectrum signal,CSm2. In response to receiving the 4th node-identification code, themaster unit derives a master unit spectrum spreading communication codefor the 4th slot from the 4th node-identification code, and uses it togenerate a master unit 4th slot communication spread spectrum signal,CMN4. The 4th master unit slot communication signal, CMN4, is then usedfor all transmissions from the master unit to the 4th node unit.

75. If all node units utilize the same receive spread spectrum code(CMN4), the master unit does not necessarily have to derive a spectrumspreading code from the 4th node unit's identification code, but mayrather, upon determination by the master unit that the 4th node unit'sidentification code is valid, transmit a spread spectrum communicationsignal common to all node units able to access the master and rely onaddress bits within the time slot to maintain synchronization of thefour node units with the master unit.

76. In response to receiving the master-identification code for the 4thtime slot, the 4th node unit derives a 4th node unit spectrum spreadingcommunication code from the master-identification code, and uses it togenerate a 4th node unit communication spread spectrum signal, CNM4. The4th node unit communication signal, CNM4, is then used for alltransmissions from the 4th node unit to the master unit.

77. In a particular embodiment, as illustrated in FIG. 4, there may be4000 samples per second, divided into 1000 frames of four time slots of250 microseconds each, allowing N=4 users to use one time slot 1000times per second. The master unit transmits eighteen bits (twooverhead/addressing, sixteen data) in each time slot it uses, yielding16 kbps throughput from the master unit to each node unit per slot,which may be applied as compressed digital voice for a cordlesstelephone application. In initialization or identification modes, theeighteen bits may be used differently. Node units, which may be embodiedas handsets as illustrated in FIG. 1, transmit eighteen bits per timeslot only in response to receiving a spread spectrum initialization,identification, or communication signal from the master unit. The masterunit transmission frame comprises four time slots, and is configuredsuch that it does not transmit in a time slot except to send a spreadspectrum communication signal to K users who are on line, plus aninitialization (in the case of a search for a new node unit trying toaccess the master unit) or identification (in the case of a new nodeunit in the process of accessing a master unit) signal, leaving N-K-1time slots open. If the master unit is transmitting amaster-identification spread spectrum signal in the (K+1)th time slot(i.e. the (K+1)th node unit is accessing the system), it then maytransmit a master-initialization spread spectrum signal in the (K+2)thtime slot, in order to allow the (K+2)th node unit to access the masterunit. Thus, if two node units are present, then the master unittransmits in the first through second time slots the communicationspread spectrum signals pertaining to the first through second nodes,and in the third time slot an initialization spread spectrum signalcommon to all node units that may access the master unit, which may bedistinct from all communication and identification spread spectrumsignals.

78. If, with N=4 and K=2 node units, a plurality of up to 2 node unitstry to access the master unit sequentially in time, with the periodbetween access attempts being greater than or equal to the slot period,or 250 microseconds, upon reception of the master-initialization spreadspectrum signal, CSn1, the third and fourth node units will access thethird and fourth time slots, respectively, immediately available in thefirst time frame following their respective initiations of the accessattempt. When the third node unit has accessed the system (master unitslot and third node unit identification signals are being transmitted inthe third time slot), the master unit may wait to transmit the fourthmaster unit slot identification signal until the third slot is occupiedwith master unit-to-3rd node unit and/or third node unit-to-master unitcommunication signals. If, with N=4 and K=2 node units, a plurality ofup to two node units tries to access the master unit instantaneously(the time period between node unit access attempts being less than theslot period, or 250 microseconds), upon reception of themaster-initialization spread spectrum signal, CSn1, in the third timeslot, the third and fourth node units will transmit a firstnode-initialization spread spectrum signal, CSm1, within the third timeslot, thus jamming at least one of the first node-initializationsignals, CSm1, at the master unit. If the master unit does not receive avalid initialization signal, CSm, or identification code from a nodeunit during the third slot, it may cease to transmit any signal in thethird time slot for a predetermined period of time, or it may transmit a“jammed signal alarm” code through the master-identification spreadspectrum signal, CSn2. When a lack of response or a jammed signal alarmcode from the master unit is encountered, the third and fourth nodeunits may then initiate a node unit internal “wait” state, whose periodmay be derived from each node unit's identification code. After the waitstate period, the third and fourth node units may attempt to access itagain. Since wait states may be highly unique to each node unit, it isunlikely that the third and fourth node will units jam each other again.If all four time slots are being used for communication orinitialization functions by four node units, then the initializationspread spectrum signal, CSn1, is not transmitted by the master unit, andno new node units of the plurality of X−4 node units may access themaster unit.

79. With N=4 and K=2, the master unit may function with theinitialization, identification, and communication procedures detailedabove, but may be configured to transmit the master-initializationspread spectrum signal, CSn1, in the vacant the third and fourth timeslots. If the master unit does transmit the third and fourth vacant timeslots, node units three and four may access the master unit in the thirdand fourth time slots, respectively or randomly. Therefore, the thirdnode unit trying to access the master unit would access the first timeslot immediately available after its initiation of the access attempt,instead of waiting for the third time slot to occur in the next frame.

80. Thus, if two users are present, the master unit transmits in thefirst through second time slots the master unit communication spreadspectrum signals, CMN1 through CMN2, pertaining to the first throughsecond node units, and in the third through fourth time slots a masterinitialization spread spectrum signal, CSn1, common to the plurality, X,of node units that may access the master unit, which may be distinctfrom all master or node unit communication and identification spreadspectrum signals. If two node units try to access the master unitsequentially in time, with the period between access attempts beinggreater than or equal to the slot period of 250 microseconds, uponreception of the master-initialization spread spectrum signal, CSn1,each node unit will access the open time slot available immediatelyfollowing its initiation of the access attempt. When the third node unithas accessed the master unit (master unit slot and third node unitidentification signals are being transmitted in the third time slot),the master unit may wait to transmit the fourth master unit slotidentification signal until the third slot is occupied with masterunit-to-4th node unit and/or third node unit-to-master unitcommunication signals.

81. If a plurality of up to two node units tries to access the masterunit instantaneously (the time period between node unit access attemptsbeing less than the slot period, or 250 microseconds), upon reception ofthe master-initialization spread spectrum signal, CSn1, the third andfourth node units will transmit a first node-initialization spreadspectrum signal, CSM1, or second node-initialization spread spectrumsignal, CSm2, within the same time slot, thus jamming at least one ofthe node-initialization spread spectrum signal or node-identificationspread spectrum signal, CSm, at the master unit. If the master unit doesnot receive a valid node-initialization spread spectrum signal ornode-identification spread spectrum signal, CSm1, or identification codefrom a node unit during the time slot, it may cease to transmit anysignal in that time slot for a predetermined period of time, or it maytransmit a “jammed signal alarm” code through the master-identificationspread spectrum signal, CSn2. When a lack of response or a jammed signalalarm code from the master unit is encountered, the third and fourthnode units may initiate a node unit internal “wait” state, whose periodmay be derived from each node unit's identification code. After the waitstate period, the third and fourth node units may attempt to access itagain. Since wait states may be highly unique to each node unit, it isunlikely that the third and fourth node units will jam each other again.

82. The timing structure illustrated in FIG. 4 for the communicationmode serves as example only, and is not intended to be restrictive in orto the current embodiment of the invention. The number of address,overhead, and data bits, turnaround, delay, and transmitter turn-on/offtimes, bit periods, samples, frames and/or slots per second may bedifferent according to the operational mode the system is in (i.e.initialization, identification, communication) as well as the specificimplementation of the invention.

83. In another embodiment, as illustrated in FIG. 5, the system operatesas in the first embodiment (i.e. node units transmit only in response toa master unit transmission of the node unit's code, the K and N-K slotsoperating the same, etc.) except that the master and node transmit M-arydata bits per code sequence. In this embodiment, there may be 25000samples per second, divided into 1000 frames per second of 25 time slotsof 40 microseconds each, allowing N=25 users to use one time slot 1000times per second. (See FIG. 5.) The master unit transmits 22 binary databits (6 overhead/addressing, 16 data) in quarternary operation, whereeach code sequence transmission represents two binary data bits, or fourbinary states, which may be represented as: Code Sequence Number DataBits 0 00 1 01 2 10 3 11

84. The master-node link therefore yields 16 kbps throughput per slot.In initialization or identification nodes, the data structure of thetransmission may be different in order for the handshaking operations tobe completed. Node units, which may be embodied as handsets illustratedin FIG. 1, transmit 22 binary data bits in each time slot (6overhead/addressing, 16 data) in 16-ary operation, wherein each codesequence transmission represents four binary data bits, or sixteenbinary states, which may be represented as: Code Sequence Number DataBits 0 0000 1 0001 2 0010 3 0011 4 0100 5 0101 6 0110 7 0111 8 1000 91001 10 1010 11 1011 12 1100 13 1101 14 1110 15 1111

85. The node-master unit link therefore yields 16 kbps throughput perslot. In initialization or identification nodes, the data structure ofthe transmission may be different in order for the handshakingoperations to be completed.

86. The timing structure illustrated in FIG. 5 for the communicationmode serves as example only, and is not intended to be restrictive in orthe current embodiment of the invention. The number of address,overhead, and data bits, turnaround, delay, and transmitter turn-on/offtimes, bit period, m-ary operations, samples, frames and/or slots persecond may be different according to the operational mode the system isin (i.e. initialization, identification, communication) as well as thespecific implementation of the invention.

87. There are obvious advantages to the M-ary approach. One is more nodeunits per master unit for the same bandwidth. Another is lower receivercomplexity in the node units, which allows for a more practicalimplementation in handheld, battery powered devices such as telephones.For example, in the current embodiment, the node receiver could storefewer spread spectrum codes, reducing its complexity, relying on themaster unit to contain more spread spectrum codes and complexity.

88. The present invention allows for multiple base stations to besituated closely together through the use of frequency offsets in athree frequency zone architecture, as illustrated in FIG. 6. By relyingon code division multiplexing, frequency re-use can be employed in everyother zone. This requires that node units be able to scan the threefrequencies to determine which is used by the master unit whose zone thenode is in.

89. In a second embodiment of the present invention, a fixed, or Fth,time slot, such as the 1st or Nth slots of the plurality of N time slotsin a time frame, serves as the access slot. The second method andapparatus comprises the steps of transmitting in the Fth time slot fromthe master unit the master-initialization spread spectrum signal, CSn1,common to all node units. The Fth time slot may occupy a fixed time slotwithin the time frame of the N-K unused time slots, and does not changeslots as the number, K, of node units which have establishedcommunications links with the master unit, changes.

90. In response to receiving the master-initialization spread spectrumsignal, CSn1, in the Fth time slot, the (K+1)th node unit transmits inthe Fth time slot a (K+1)th node-initialization spread spectrum signal,CSm, which may be the same as CSn1, common to all master units that the(K+1)th node unit may access, which may contain the (K+1)th node unit'sidentification code.

91. The master unit receives the node-initialization spread spectrumsignal, CSm, in the Fth time slot from the (K+1)th node unit, andtransmits in the Fth time slot a master-identification spread spectrumsignal, CSn2, which may be distinct from spread spectrum signal CSn1 butcommon to all X node units, containing the master unit's (K+1)th slotidentification code, which may include information directing the (K+1)thnode unit as to which time slot and spectrum spreading code to use forcommunication from the (K+1)th node unit to the master unit.

92. In response to receiving the master-identification spread spectrumsignal, CSn2, the (K+1)th node unit may transmit in the Fth time slotthe (K+1)th node-initialization spread spectrum signal, CSm, common toall master units that it may access, which may contain its (K+1)th nodeunit identification code, which may have a high degree of uniqueness tothe plurality of the N−1 other node units.

93. The master unit receives the (K+1)th node unit's identification codefrom the (K+1)th node unit in the Fth time slot via thenode-initialization spread spectrum signal, CSm, common to all masterunits accessible by the (K+1)th node unit, and transmits in the (K+1)thtime slot a master unit (K+1)th slot communication spread spectrumsignal, CMNk+1, generated from a spectrum spreading code derived fromthe (K+1)th node unit's identification code.

94. In response to receiving the (K+1)th master unit identification codefrom the master unit in the Fth time slot via the master-identificationspread spectrum signal, CSn2, common to all X node units, the (K+1)thnode unit transmits in the (K+1)th time slot a (K+1)th node unitcommunication spread spectrum signal, CNMk+1, generated from a spectrumspreading code derived from the (K+1)th master-identification code.

95. As an alternative architecture of the second embodiment, the (K+1)thnode unit may transmit the (K+1)th node communication spread spectrumsignal in the (K+1)th time in slot in response to receiving the masterunit (K+1)th slot communication signal in the (K+1)th time slot. In thiscase, the master-identification spread spectrum signal transmitted inthe Fth time slot would not necessarily contain information detailingwhich time slot of the N-K time slots to use for communicationtransmissions.

96. In the second embodiment, the master unit may operate such that itdoes not transmit in a time slot except to send a plurality of K masterunit slot communication spread spectrum signals, CMN1 to CMNK, to K nodeunits which have established communications links with the master unit,plus a master-initialization spread spectrum signal, CSn1, in the caseof a search for a new node unit trying to access the master unit, or amaster-identification spread spectrum signal, CSn2, in the case of anode unit being in the process of accessing a master unit, in the Fthtime slot, leaving N-K-1 time slots unused. If the master unit istransmitting a master-identification spread spectrum signal, CSn2, inthe Fth time slot (assuming the (K+1)th node unit is in the process ofaccessing the system), it then may transmit a master initializationspread spectrum signal, CSn1, in one of the N-K-1 unused time slots, inorder to allow the (K+2)th node unit to access the master unit.

97. If a plurality of up to N-K node units tries to access the masterunit sequentially in time, with the period between access attempts beinggreater than or equal to the frame period, upon reception of themaster-initialization spread spectrum signal, CSn1, each node unit ofthe plurality of N-K node units will access the (K+1)th time slotthrough the Fth time slot immediately available following its initiationof the access attempt. When the first (K+1)th node unit has accessed thesystem (assuming the master-identification and (K+1)thnode-identification spread spectrum signals are being transmitted in theFth time slot), the master unit may wait to transmit the (K+2)thmaster-identification spread spectrum signal until the (K+1)th slot isoccupied with master unit-to-(K+1)th node unit and/or (K+1)th nodeunit-to-master unit communication signals.

98. If a plurality of up to N-K node units tries to access the masterunit instantaneously (the time period between node unit access attemptsbeing less than the frame period), upon reception of themaster-initialization spread spectrum signal, CSn1, in the Fth timeslot, each node unit of this plurality of anode units will transmit anode-initialization spread spectrum signal, CSm, within the same timeslot, thus jamming at least one of the node-initialization spreadspectrum signals, CSm, at the master unit. If the master unit does notreceive a valid initialization signal, CSm, or identification code froma node unit during the time slot, it may cease to transmit any signal inthe Fth time slot for a predetermined period of time, or it may transmita “jammed signal alarm” code through the master-identification spreadspectrum signal, CSn2. When a lack of response or a jammed signal alarmcode from the master unit is encountered, the node units which tried toaccess the master unit instantaneously, of the plurality, N-K, of nodeunits, may then initiate a node unit internal “wait” state, whose periodmay be derived from each node unit's identification code. After the waitstate period, the plurality of node units which failed to access themaster unit may attempt to access it again. Since wait states may behighly unique to each node unit, it is unlikely that the same pluralityof node units will jam each other again.

99. If all N−1 time slots are being used for communication orinitialization functions by N−1 node units, then themaster-initialization spread spectrum signal, CSn1, is not transmitted.The master unit may operate such that the Fth time slot may a “busy”alarm to the plurality of N-K node units having not establishedcommunications with the master unit such that it informs them that nofurther access is available at that master unit, thereby allowing onlyN−1 node units to access the master unit.

100. In a third embodiment of the present invention, the master unit mayfunction with the initialization, identification, and communicationprotocols as set forth in the first and second embodiments, but may beconfigured to transmit the master-initialization spread spectrum signal,CSn1, in a plurality of vacant (N-K) time slots, simultaneously. If themaster unit does transmit in a plurality of vacant (N-K) time slots,node units (K+1), (K+2), (K+3), . . . , (K+(N-K) (or N) may access themaster unit in the (K+1)th, (K+2)th, (K+3)th, . . . , (K+(N-K))th (orNth) time slots, respectively or randomly. Therefore, the (K+1)th nodeunit trying to access the master unit would access the first time slotimmediately available after its initiation of the access attempt,instead of waiting for the (K+1)th or Fth time slot to occur in the nextframe.

101. Thus, if K users are present, the master unit transmits in the 1stthrough Kth time slots the master unit communication spread spectrumsignals, CMN1 through CMNk, pertaining to the 1st through Kth nodeunits, and in the (K+1)th through Nth time slots a master initializationspread spectrum signal, CSn1, common to the plurality, X, of node unitsthat may access the master unit, which may be distinct from all masteror node unit communication and identification spread spectrum signals.

102. If a plurality of up to N-K node units tries to access the masterunit sequentially in time, with the period between access attempts beinggreater than or equal to the slot period, upon reception of themaster-initialization spread spectrum signal, CSn1, each node unit willaccess the open time slot available immediately following its initiationof the access attempt. When the first (K+1)th node unit has accessed themaster unit (master unit slot and (K+1)th node unit identificationsignals are being transmitted in the (K+1)th time slot), the master unitmay wait to transmit the (K+2)th through Nth master unit slotidentification signals until the (K+1)th slot is occupied with masterunit-to-(K+1)th node unit and/or (K+1)th node unit-to-master unitcommunication signals.

103. If a plurality of up to N-K node units tries to access the masterunit instantaneously (the time period between node unit access attemptsbeing less than the slot period), upon reception of themaster-initialization spread spectrum signal, CSn1, each node unit ofthis plurality of node units will transmit a node-initialization spreadspectrum signal, CSm, within the same time slot, thus jamming at leastone of the node-initialization spread spectrum signals, CSm, at themaster unit. If the master unit does not receive a validnode-initialization spread spectrum signal, CSm, or identification codefrom a node unit during the time slot, it may cease to transmit anysignal in that time slot for a predetermined period of time, or it maytransmit a “jammed signal alarm” code through the master unit slotidentification signal, CSn2. When a lack of response or a jammed signalalarm code from the master unit is encountered, the node units whichtried to access the master unit Instantaneously, of the plurality, N -K, of node units, may initiate a node unit internal “wait” state, whoseperiod may be derived from each node unit's identification code. Afterthe wait state period, the plurality of node units which failed toaccess the master unit may attempt to access it again. Since wait statesmay be highly unique to each node unit, it is unlikely that the sameplurality of node units will jam each other again.

104. If all N time slots are being used for communication orinitialization functions by N node units, then the initialization spreadspectrum signal, CSn1, is not transmitted by the master unit, and no newnode units of the plurality of X - N node units may access the masterunit. The master unit may operate such that the Nth time slot maytransmit a “busy” alarm to the plurality of N-K node units having notestablished communications with the master unit such that it informsthem that no further access is available at that master unit, therebyallowing only N−1 node units to access the master unit.

105. It will be apparent to those skilled in the art that variousmodifications can be made to the method for establishing spread spectrumcommunications between a master unit and a plurality of node units ofthe present invention, without departing from the scope or spirit of theinvention, and it is intended that the present invention covermodifications and variations of the method for establishing spreadspectrum communications as described herein, provided they come withinthe scope of the appended claims and their equivalents.

We claim:
 1. A method for establishing communications between a unit anda plurality of N node units wherein K node units of said plurality ofnode units have established communications channels with said masterunit using upto 2K different spread spectrum codes, respectively, with atime slot for each the the K node units in the first K time slots,respectively, and a first node unit of the N-K node units of saidplurality of said node units, desires to establish communications withsaid master unit, comprising the steps of: transmitting, in a (K+1)^(th)time slot from said master unit, a master-initialization spread spectrumsignal modulated by a master-common-signalling chip code; transmitting,in the (K+1)^(th) time slot from said first node unit, responsive toreceiving the master-initialization spread spectrum signal at said firstnode unit, a first node-initialization spread spectrum signal;transmitting, in the (K+1)^(th) time slot from said master unit,responsive to receiving the first node-initialization spread spectrumsignal at said master unit, a master-identification spread spectrumsignal with a master-unit-slot-identification code, modulated by themaster-common-signalling chip code having a master-identification code;transmitting, in the (K+1)^(th) time slot from said first node unit,responsive to receiving the master-identification spread spectrum signalat said first node unit, a second node-initialization spread spectrumsignal modulated by a (K+1)-node-identification code and themaster-common-signalling chip code; generating, at said first node unitusing the master identification code, a master unit chip code fortransmitting spread spectrum signals to said master unit; generating, atsaid master unit using the (K+1)-node-identification code, a(K+1)-node-unit chip code for transmitting: spread spectrum signals tosaid first node unit; and communicating from said master unit using the(K+1)-node-unit chip code to said first node unit, and from said firstnode unit using the master unit chip code to said master unit, in the(K+1)^(th) time slot.
 2. A method for establishing communicationsbetween a master unit and a first node unit comprising the steps of:transmitting, a master-initialization spread spectrum signal modulatedby a master-common-signalling chip code; transmitting, responsive toreceiving the master-initialization spread spectrum signal at said firstnode unit, a first node-initialization spread spectrum signal;transmitting, responsive to receiving the first node-initializationspread spectrum signal at said master unit, a master-identificationspread spectrum signal having a master-unit-slot-identification codemodulated by the master-common-signalling chip code having amaster-identification code; transmitting, responsive to receiving themaster-identification spread spectrum signal at said first node unit, asecond node-initialization spread spectrum signal modulated by a firstidentification code and the master-common-signalling chip code of themaster-initialization spread spectrum signal; generating, at saidfirst-node unit using the master identification spread spectrum signal,a master unit chip code for transmitting spread spectrum signals to saidmaster unit.
 3. The method as set forth in claim 2 further comprisingthe steps, using a second node unit, of: transmitting, responsive toreceiving the master-initialization spread spectrum signal at saidsecond node unit, a third node-initialization spread spectrum signal;transmitting, responsive to receiving the second node-initializationspread spectrum signal at said master unit, a master-identificationspread spectrum signal having the master-unit slot-identification code;transmitting, responsive to receiving the master-identification spreadspectrum signal at said second node unit, a fourth node-initializationspread spectrum signal modulated by a (K+2)-node-identification code andthe master-common-signalling chip code; generating, at said second nodeunit using the master-identification code, a second master unit chipcode for transmitting spread spectrum signals to said master unit; andgenerating, at said master unit using the (K+2)-node-identificationcode, a (K+2)-node-unit chip code for transmitting spread spectrumsignals to said second node unit.
 4. A system for establishingcommunications between a master unit and a plurality of N node unitswherein K node units of said plurality of node units have establishedcommunications channels with said master unit using upto 2K differentspread spectrum codes, respectively, with a time slot for each the the Knode units in the first K time slots, respectively, and a first nodeunit of the N-K node units of said plurality of said node units, desiresto establish communications with said master unit, comprising: means,located at said master unit, for transmitting, in a (K+1)^(th) time slotfrom said master unit, a master-initialization spread spectrum signalmodulated by a master-common-signalling chip code; means, located atsaid first node unit and responsive to receiving themaster-initialization spread spectrum signal at said first node unit,for transmitting, in the (K+1)^(th) time slot from said first node unit,a first node-initialization spread spectrum signal; means, located atsaid master unit and responsive to receiving the firstnode-initialization spread spectrum signal at said master unit, fortransmitting in the (K+1)^(th) time slot from said master unit, amaster-identification spread spectrum signal with amaster-unit-slot-identification code, modulated by themaster-common-signalling chip code having a master-identification code;means located at said first node unit and responsive to receiving themaster-identification spread spectrum signal at said first node unit,for transmitting, in the (K+1)^(th) time slot from said first node unit,a second node-initialization spread spectrum signal modulated by a(K+1)-node-identification code and the master-common-signalling chipcode; means, located at said first node unit and using the masteridentification code, for generating a master unit chip code fortransmitting spread spectrum signals to said master unit; mean, locatedat said master unit and using the (K+1)-node-identification code, forgenerating a (K+1)-node-chip code for transmitting spread spectrumsignals to said first node unit; means located at said master unit forcommunicating from said master unit using the (K+1)-node-unit chip code,in the (K+1)^(th) time slot; and means located at said first node unitfor communicating from said first node unit using the master unit chipcode, in the (K+1)^(th) time slot.
 5. A system for establishingcommunications between a master unit and a first node unit, comprising:means, located at said master unit, for transmitting amaster-initialization spread spectrum signal modulated by amaster-common-signalling chip code; means, located at said first nodeunit and responsive to receiving the master-initialization spreadspectrum signal, for transmitting a first node-initialization spreadspectrum signal; means, located at said master unit and responsive toreceiving the first node-initialization spread spectrum signal, fortransmitting a master-identification spread spectrum signal with amaster-unit-slot-identification code, modulated by themaster-common-signalling chip code having a master-identification code;means located at said first node unit and responsive to receiving themaster-identification spread spectrum signal, for transmitting a secondnode-initialization spread spectrum signal modulated by a(K+1)-node-identification code and the master-common-signalling chipcode; means, located at said first node unit and using the masteridentification code, for generating a master unit chip code fortransmitting spread spectrum signals to said master unit; mean, locatedat said master unit and using the first identification code, forgenerating a (K+1)-node-unit chip code for transmitting spread spectrumsignals to said first node unit; means located at said master unit forcommunicating from said master unit using the (K+1)-node-unit chip code,in the (K+1)^(th) time slot; and means located at said first node unitfor communicating from said first node unit using the master unit chipcode, in the (K+1)^(th) time slot.
 6. The system as set forth in claim 5using a second node unit comprising: means located at said second nodeunit and responsive to receiving the master-initialization spreadspectrum signal at said second node unit, for transmitting a thirdnode-initialization spread spectrum signal; means located at said masterunit and responsive to receiving the third node-initialization spreadspectrum signal, for transmitting a master-identification spreadspectrum signal having the master-slot-identification code modulated bythe master-common-signalling chip code having a master-identificationcode; means located at said second node unit and responsive to receivingthe master-identification spread spectrum signal, for transmitting afourth node-initialization spread spectrum signal modulated by a(K+2)-node-identification code and the master-common-signalling chipcode; means located at said second node unit using themaster-identification code, for generating a second master unit chipcode for transmitting spread spectrum signals to said master unit; andmeans located at said master unit using the second identification code,for generating a (K+2)-node-unit chip code for transmitting spreadspectrum signals to said second node unit.
 7. A method for establishingcommunications between a master unit and a plurality of N node unitswherein K node units of said plurality of node units have establishedcommunications channels with said master unit using upto 2K differentspread spectrum codes, respectively, with a time slot for each the the Knode units in the first K time slots, respectively, and a first nodeunit of the N-K node units of said plurality of said node units, desiresto establish communications with said master unit, comprising the stepsof: transmitting, in a (K+1)^(th) time slot from said master unit, amaster-initialization spread spectrum signal modulated by amaster-common-signalling chip code; transmitting, in the (K+1)^(th) timeslot from said first node unit, responsive to receiving themaster-initialization spread spectrum signal at said first node unit, anode-identification spread spectrum signal modulated by a(K+1)-node-identification code and the node-common-signalling chip code;transmitting, in the (K+1)^(th) time slot from said master unit,responsive to receiving the first node-initialization spread spectrumsignal at said master unit, a master-identification spread spectrumsignal with a master-unit-slot-identification code, modulated by themaster-common-signalling chip code having a master-identification code;generating, at said first node unit using the master identificationcode, a master unit chip code for transmitting spread spectrum signalsto said master unit; generating, at said master unit using the(K+1)-node-identification code, a (K+1)-node-unit chip code fortransmitting spread spectrum signals to said first node unit; andcommunicating from said master unit using the (K+1)-node-unit chip code,and from said first node unit using the master unit chip code, in the(K+1)^(th) time slot.
 8. A method for establishing communicationsbetween a master unit and a first node unit comprising the steps of:transmitting from said master unit a master-initialization spreadspectrum signal modulated by a master-common-signalling chip code;transmitting, responsive to receiving the master-initialization spreadspectrum signal at said first node unit, a first node-identificationspread spectrum signal modulated by a first identification code;transmitting, responsive to receiving the first node-identificationspread spectrum signal at said master unit, a master-identificationspread spectrum signal having a master-unit-slot-identification code;generating, at said first node unit using the master identificationcode, a master unit chip code for transmitting spread spectrum signalsto said master unit; generating, at said master unit using the(K+1)-node-identification code, a (K+1)-node-unit chip code fortransmitting spread spectrum signals to said first node unit; andcommunicating from said master unit using the (K+1)-node-unit chip code,and from said first node unit using the master unit chip code.
 9. Themethod as set forth in claim 8 further comprising the steps, using asecond node unit, of: transmitting, responsive to receiving themaster-initialization spread spectrum signal at said second node unit, asecond node-unit-identification spread spectrum signal modulated by asecond identification code; transmitting, responsive to receiving thesecond node-unit-identification spread spectrum signal at said masterunit, a master-identification spread spectrum signal having themaster-unit-identification code; generating, at said second node unitusing the master-identification code, a second master unit chip code fortransmitting spread spectrum signals to said master unit; andgenerating, at said master unit using the (K+1)-node-identificationcode, a (K+2)-node-unit chip code for transmitting spread spectrumsignals to said second node unit.
 10. A system for establishingcommunications between a master unit and a plurality of N node unitswherein K node units of said plurality of node units have establishedcommunications channels with said master unit using upto 2K differentspread spectrum codes, respectively, with a time slot for each the the Knode units in the first K time slots, respectively, and a first nodeunit of the N-K node units of said plurality of said node units, desiresto establish communications with said master unit, comprising: means,located at said master unit, for transmitting, in a (K+1)^(th) time slotfrom said master unit, a master-initialization spread spectrum signalmodulated by a master-common-signalling chip code; means, located atsaid first node unit and responsive to receiving themaster-identification spread spectrum signal at said first node unit,for transmitting, in the (K+1)^(th) time slot from said first node unit,a node-identification spread spectrum signal modulated by a firstidentification code and the master-common-signalling chip code of themaster-initialization spread spectrum signal; means, located at saidmaster unit and responsive to receiving the first node-identificationspread spectrum signal at said master unit, for transmitting in the(K+1)^(th) time slot from said master unit, a master-identificationspread spectrum signal with a master-unit-slot-identification code,modulated by the master-common-signalling chip code having amaster-identification code; means, located at said first node unit andusing the master identification code, for generating a master unit chipcode for transmitting spread spectrum signals to said master unit; mean,located at said master unit and using the (K+1)-node-identificationcode, for generating a (K+1)-node-chip code for transmitting spreadspectrum signals to said first node unit; means located at said masterunit for communicating from said master unit using the (K+1)-node-unitchip code, in the (K+1)^(th) time slot; and means located at said firstnode unit for communicating from said first node unit using the masterunit chip code, in the (K+1)^(th) time slot.
 11. A system forestablishing communications between a master unit and a first node unit,comprising: means, located at said master unit, for transmitting amaster-initialization spread spectrum signal modulated by amaster-common-signalling chip code; means, located at said first nodeunit and responsive to receiving the master-initialization spreadspectrum signal, for transmitting, a first node-identification spreadspectrum signal modulated by a first identification code; means, locatedat said master unit and responsive to receiving the firstnode-identification spread spectrum signal, for transmitting amaster-identification spread spectrum signal with amaster-unit-slot-identification code; means, located at said first nodeunit and using the master-identification code for generating a masterunit chip code for transmitting spread spectrum signals to said masterunit; mean, located at said master unit and using the firstidentification code, for generating a (K+1)-node-unit chip code fortransmitting spread spectrum signals to said first node unit; meanslocated at said master unit for communicating from said master unitusing the (K+1)-node-unit chip code, in the (K+1)^(th) time slot; andmeans located at said first node unit for communicating from said firstnode unit using the master unit chip code, in the (K+1)^(th) time slot.12. The system as set forth in claim 11 using a second node unit furthercomprising: means located at said second node unit and responsive toreceiving the master-initialization spread spectrum signal at saidsecond node unit, for transmitting a second node-identification spreadspectrum signal modulated by a second identification code; means locatedat said master unit and responsive to receiving the secondnode-identification spread spectrum signal, the master-identificationspread spectrum signal having the master-unit-identification code; meanslocated at said second node unit using the master-identification code,for generating a second master unit chip code for transmitting spreadspectrum signals to said master unit; and means located at said masterunit using the (K+1)-node-identification code, for generating a(K+2)-node-unit chip code for transmitting spread spectrum signals tosaid second node unit.